This invention relates to a method of applying a protective coating to a touch screen panel and in particular to using infrared radiation to more fully densify the protective coating.
Touch screens are now ubiquitous and used as the input and display interface at, for example, automatic teller machines, gambling machines in casinos, cash registers, and the like.
To protect the substrate of the touch screen from scratches, a protective coating is often applied to the substrate in liquid form and then cured in an oven.
One problem with preferred coating compositions, however, is that the temperature at which they undergo full curing can not be tolerated by the glass substrate of the touch screen panel.
For example one protective coating composition cures at about 800xc2x0 C. and yet the maximum temperature the glass substrate can withstand is about 550xc2x0 C. before it experiences thermal damage.
To compensate, the protective coating is xe2x80x9ccuredxe2x80x9d in an oven set at a temperature lower than specified but for an extremely long period of time.
The result is that the protective coating never reaches fill densification, is often not properly bonded to the substrate, and does not offer optimum abrasion resistance. Also, the cost of the touch screen increased due to the long dwell time required for the curing step where the protective coating is densified.
It is therefore an object of this invention to provide an improved method of forming a coating on a touch screen panel.
It is a further object of this invention to provide such a method in which the protective coating achieves a higher level of densification.
It is a further object of this invention to provide such a method in which the protective coating achieves a higher level of densification without subjecting the glass substrate and/or the conductive coating thereon of the touch screen panel to thermal damage.
It is a further object of this invention to provide such a method which results in optimum abrasion resistance for the touch screen panel.
It is a further object of this invention to provide such a method which reduces the curing time of the protective coating and thus the cost of touch screen panels.
It is a further object of this invention to provide such a method which insures the protective coating is properly bonded to the touch screen panel substrate.
This invention results from the realization that a higher level of densification and a more abrasion resistant touch screen panel can be manufactured in a shorter period of time without damaging the panel by irradiating the coating material with infrared radiation which better cures the coating material and yet does not raise the temperature of the panel to a temperature which would cause it thermal damage.
This invention features a method of applying a protective coating to a touch screen panel. The method comprises applying to a touch screen panel on at least one surface thereof a coating material which cures at an elevated temperature; heating the panel to a temperature which does not adversely affect the panel by irradiating the panel imparting energy to the coating material to more fully cure the coating material in a shorter time period without damaging the panel.
The preferred coating material is a silicate polymer solution. The step of applying the coating material is typically performed by spin coating, dip coating, spray coating, meniscus coating, flow coating, screen printing, or roll coating. Irradiating is preferably accomplished by infrared radiation sources which emit radiation at wavelengths in the range of between 2.5 and 6.0 microns.
The silicate polymer solution is preferably a silicate solution synthesized from the hydrolysis and condensation of silicon alkoxides. The silicate polymer solution may include sodium acetate, water, tetraethoxsilane, methyltriethoxysilane, isopropanol, and ethanol.
The infrared radiation source may be an array of externally wound quartz heater tubes but heating may include both irradiation and convective heating at the same time and in the same oven. Typically, heating takes place in an oven equipped with infrared heaters disposed over a conveyor which transports the coated touch screen panels. The oven may be equipped with externally wound quartz heater tubes for irradiating the touch screen panels with infrared radiation and further equipped with refractory heaters for convectively heating the touch screen panels.